The invention relates to a method of manufacturing an electron beam tube for displaying television pictures, which tube is provided with a glass envelope having a substantially rectangular display window on which phosphor patterns are present, and a colour selection electrode facing these patterns. More particularly, the invention relates to such a method in which a lacquer layer is provided on the patterns and an aluminium layer is provided on the lacquer layer, whereafter the lacquer layer is removed and the aluminium layer is left on the patterns, and an electrically conducting contact is obtained between the patterns and the colour selection electrode via a strip-shaped electrically conducting graphite layer and the aluminium layer.
A method of the type described in the opening paragraph in known, for example, from U.S. Pat. No. 4,301,041.
In a method of the type described in the opening paragraph, patterns of red, green and blue phosphors are provided on the display window in a conventional manner. A lacquer layer and an aluminium layer are successively provided on these patterns. The aluminium layer is used inter alia to prevent charging of the display window and for reflection of the light emitted by the phosphors.
The lacquer layer is used to establish a satisfactory coating of the phosphor patterns by the aluminium layer. In a thermal treatment after the provision of the aluminium layer, taking place, for example, when the display window and the cone are sealed, the lacquer layer is removed.
A conducting contact must be provided between the colour selection electrode and the aluminium layer. As is common practice, a layer of a graphite suspension in the form of a strip is used for this purpose, one end of which strip is provided on the aluminium layer, and the other end extends as far as, for example, suspension pins of the colour selection electrodes, which pins are sealed on the wall of a raised edge of the display window.
In this respect it is to be noted that the graphite strip is needed because the aluminium film which is provided by vapour deposition does not provide satisfactory contacts with the suspension pins.
However, when the lacquer layer, the aluminium layer and the graphite layer are successively provided and when subsequently the lacquer layer is removed by a thermal treatment, the graphite layer is interrupted because the underlying lacquer layer impedes the adhesion of the graphite layer to the glass wall in areas where the aluminium layer is absent.
Consequently, the lacquer layer must be removed prior to providing the graphite layer. For this purpose, either an additional thermal treatment is required or it is necessary to add solvents dissolving the lacquer layer to the graphite suspension, or the lacquer layer must be removed by another process, for example, a mechanical process.
Providing the graphite layer prior to providing the lacquer layer is no solution because graphite layers of the conventional composition are attacked by solvents used for the lacquer layer.
It is an object of the invention to obviate the described problem at least to a considerable extent. The invention is based inter alia on the recognition that a graphite layer having a suitable composition can contribute to realising this object.